In an insertion system known from EP-A1-04 77 877, a positive feed mechanism is provided downstream of a measuring feeder comprising an engageable stopper in the yarn path towards the jet insertion device of the jet loom. The feed mechanism consists either of a pair of conveyor rollers with a stationary drivable conveyor roller and a freewheeling roller and a counter-roller which can be pressed against the driven conveyor roller during part of an insertion process, or of a stationarily supported drivable conveyor roller and an actuator which presses the weft yarn onto the conveyor roller only for some time of an insertion process. The weft yarn is positively supplied for the time of the insertion process, during which the drive is activated, exactly with the speed profile of the drive and exactly at the respective circumferential speed of the conveyor roller to the jet insertion device. The drive of the driven conveyor roller is controlled according to a predetermined speed profile to relieve the jet insertion device upon withdrawal of the weft yarn. The control of the conveyor roller drive is complicated. It is difficult to adapt the engagement of the positive supply mechanism to the insertion process and to the engagement and disengagement of the stopper.
In a friction-type yarn feed device which is known from EP-B1-03 87 546 and, for instance, used for a water or air jet loom, there are provided at least two spaced-apart drums which are partly surrounded by the weft yarn and have arranged thereinbetween partition walls offset on the lateral drum surfaces. A yarn brake which is independent of the weaving cycle and fixedly set is respectively provided upstream and downstream of the friction-type yarn feed device. The friction-type yarn feed device withdraws the weft yarn from a yarn coil and supplies it with a slip to the jet loom as soon as the tension produced in the jet loom and prevailing in the weft yarn overcomes the braking effect of the yarn brake arranged downstream of the friction and yarn feed device.
It is the object of the present invention to reduce the number of yarn breaks caused by extreme changes in tension in the weft yarn during operation of a jet loom and to decrease the amount of energy spent on the medium transporting the weft yarn into the shed and to increase the insertion rate without any risk of yarn breaks.
This object is achieved with the insertion system wherein a yarn brake is provided with a slip conveyor downstream of a measuring feeder or device and a yarn brake allows the slip conveyor to be deactivated.